The invention relates generally to energy storage and more specifically to the use of energy storage for multiple purposes of renewable energy sources. The invention additionally relates to wind turbines and more specifically to grid frequency flexibility in wind turbine electrical systems.
Wind turbines have bladed rotors which are connected to electrical generators by shafts. Examples of electrical generators include doubly fed induction generators (DFIGs) and permanent magnet (PM) generators. In order to feed the electrical power to the grid, power electronics elements are used for power conditioning. In one example, the power electronics elements include back-to-back voltage source converters connected to a DC link. For a DFIG, stator terminals of the generator are directly connected to the grid, and the power electronics is connected between the rotor and stator terminals. For a PM machine, AC machine terminals are connected via the power electronics.
As new grid codes are developed for wind farms, and as market penetration level of wind farms increases, variability of wind power is becoming less acceptable to utility companies. For example, utility companies are imposing or expected to impose requirements related to power ramp rate limits, low voltage ride through, power-frequency control, inertial response, and curtailment.
It would be desirable to have a system and method to efficiently address variability of wind power to help satisfy the related utility company requirements.
Wind turbines are typically designed and specified for a specific grid frequency such as 50 Hz or 60 Hz. At least two configurations are developed for each wind turbine type with one being applicable to 50 Hz and the other being applicable to 60 Hz. Typically an initial design is done for the one grid frequency and then modified for the second grid frequency. Both designs have to be certified independently. Design, engineering, parts procurement, spare parts, and training requirements are thus increased by the need for the second design and certification.
It would be desirable to have a wind turbine electrical system design that allows a flexible installation of the wind turbine regardless of grid frequency.